The First Cellular Models Based on Frataxin Missense Mutations That Reproduce Spontaneously the Defects Associated with Friedreich Ataxia

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PLoS One. 2009; 4(7): e6379.
Published online 2009 July 24. doi: 10.1371/journal.pone.0006379.
The First Cellular Models Based on Frataxin Missense Mutations That Reproduce Spontaneously the Defects Associated with Friedreich Ataxia
Nadège Calmels,#1,4,5 Stéphane Schmucker,#1,4,5 Marie Wattenhofer-Donzé,1,5 Alain Martelli,1,5 Nadège Vaucamps,1 Laurence Reutenauer,1,3 Nadia Messaddeq,1,2 Cécile Bouton,6 Michel Koenig,1,2,3,4,5 and Hélène Puccio1,2,3,4,5*
1IGBMC (Institut de Génétique et de Biologie Moléculaire et Cellulaire), Illkirch, France
2Inserm, U596, Illkirch, France
3CNRS, UMR7104, Illkirch, France
4Université de Strasbourg, Strasbourg, France
5Collège de France, Chaire de génétique humaine, Illkirch, France
6Institut de Chimie des Substance Naturelles, CNRS, Gif-sur-Yvette, France
Ellen A. A. Nollen, Editor
University Medical Center Groningen, Netherlands
#Contributed equally.
* E-mail:hpuccio@igbmc.fr

Conceived and designed the experiments: NC SS HMP. Performed the experiments: NC SS MWD AM NV LR NM CB. Analyzed the data: NC SS HMP. Wrote the paper: NC SS AM MK HMP.
Received May 11, 2009; Accepted June 25, 2009.

ABSTRACT

Background
Friedreich ataxia (FRDA), the most common form of recessive ataxia, is due to reduced levels of frataxin, a highly conserved mitochondrial iron-chaperone involved in iron-sulfur cluster (ISC) biogenesis. Most patients are homozygous for a (GAA)n expansion within the first intron of the frataxin gene. A few patients, either with typical or atypical clinical presentation, are compound heterozygous for the GAA expansion and a micromutation.
Methodology
We have developed a new strategy to generate murine cellular models for FRDA: cell lines carrying a frataxin conditional allele were used in combination with an EGFP-Cre recombinase to create murine cellular models depleted for endogenous frataxin and expressing missense-mutated human frataxin. We showed that complete absence of murine frataxin in fibroblasts inhibits cell division and leads to cell death. This lethal phenotype was rescued through transgenic expression of human wild type as well as mutant (hFXNG130V and hFXNI154F) frataxin. Interestingly, cells expressing the mutated frataxin presented a FRDA-like biochemical phenotype. Though both mutations affected mitochondrial ISC enzymes activities and mitochondria ultrastructure, the hFXNI154F mutant presented a more severe phenotype with affected cytosolic and nuclear ISC enzyme activities, mitochondrial iron accumulation and an increased sensitivity to oxidative stress. The differential phenotype correlates with disease severity observed in FRDA patients.
Conclusions
These new cellular models, which are the first to spontaneously reproduce all the biochemical phenotypes associated with FRDA, are important tools to gain new insights into the in vivo consequences of pathological missense mutations as well as for large-scale pharmacological screening aimed at compensating frataxin deficiency.